Disposable surgical drape

ABSTRACT

An improved disposable surgical drape comprising a fibrous base sheet, a fluid impervious plastic layer covering at least a portion of the base sheet, the improvement comprising a sheet of flexible, normally hydrophobic, open celled foam material bonded to the outer surface of the plastic layer, the foam material being treated with the reaction product of a mineral acid and a fatty acid tertiary amine wherein the amine is partially neutralized to a fatty acid tertiary ammonium salt which renders the foam material antistatic, while providing increased rates of fluid absorption and reduced tendency for lathering when the foam material is rubbed with water present on the foam material.

Winters [451 Sept. 2, 1975 DISPOSABLE SURGICAL DRAPE Inventor: Terry L.Winters, Neenah, Wis.

Assignee: Kimberly-Clark Corporation,

Neenah, Wis.

Filed: Apr. 5, 1974 Appl. No.: 458,315

Related US. Application Data Continuation of Ser. No. 223,990, Feb. 7,1972, abandoned.

US. Cl 128/132 D; 161/145; 161/160; 161/164; 161/165; 161/190; 161/251;260/326 N; 260/DIG. 19

Int. Cl. A6lf 13/00 Field of Search 128/132 D, 188; 161/39, 161/59,86,88,145,164,149,151,159, 161/160, 170, 190; 260/326 N, DIG. 19

References Cited UNITED STATES PATENTS Schleede et a1 128/132 D Donnelly128/132 D 3,738,359 6/1973 Lindquist et a1. 128/132 D PrimaryExaminer-Richard A. Gaudet Assistant Examiner-Henry .l. Recla Attorney,Agent, or Firm-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

An improved disposable surgical drape comprising a fibrous base sheet, afluid impervious plastic layer covering at least a portion of the basesheet, the improvement comprising a sheet of flexible, normallyhydrophobic, open celled foam material bonded to the outer surface ofthe plastic layer, the foam material being treated with the reactionproduct of a mineral acid and a fatty acid tertiary amine wherein theamine is partially neutralized to a fatty acid tertiary ammonium saltwhich renders the foam material antistatic, while providing increasedrates of fluid absorption and reduced tendency for lathering when thefoam material is rubbed with water present on the foam material.

ABSTRACT 4 Claims, 2 Drawing Figures PATENTED I 2l975 DISPOSABLESURGICAL DRAPE RELATED APPLICATIONS This is a continuation ofapplication Ser. No. 223,990, filed Feb. 7, 1972, now abandoned.

Donnelly, Ser. No. 17,431, filed Mar. 9, 1970 now U.S. Pat. No.3,668,050.

Schrading and Winters, Ser. No. 58,336, filed July 27, 1970 now U.S.Pat. No. 3,669,106.

DESCRIPTION OF THE INVENTION The present invention relates generally todisposable surgical drapes and, more particularly to surgical drapeshaving an absorbent foam material covering the primary operative area.

There have been many new commercial developments in disposable articlesfor use in hospitals, clinics, and the like, particularly with respectto surgical drapes that are intended for only a single use. Since suchdisposable surgical drapes are less expensive to initially produce,coupled with the fact that they need not be laundered and sterilized forrepeated uses has resulted in their capturing a significant commercialmarket, which is generally predicted to increase as labor costsassociated with laundering and other handling increase. Among the moresignificant recent developments in disposable surgical drapes are thosedrapes disclosed in the Donnelly application Ser. No. 17,431, filed Mar.9, 1970 now U.S. Pat. No. 3,668,050 as well as the Schrading and Wintersapplication, Ser. No. 58,336, filed July 27, 1970 now U.S. Pat. No.3,669,106 all of which are assignee to the assignee of the presentinvention.

Features common to the surgical drape disclosed in these applicationsinvolve a fibrous base sheet and a sheet of fluid impervious plasticfilm attached to the base sheet as well as a fluid absorbent plasticfoam material bonded to the plastic film in the primary operative areaof the surgical drape.

Preliminary to a detailed description of the improved surgical drape ofthe present invention, it should be pointed out that the use of opencelled foam material in at least the primary operative area, includingthe fenestration area of a laparotomy sheet for example, has experiencedwidespread acceptance, particularly when it is combined with anunderlayer of fluid impervious plastic or film, since the combination isstrong and abrasion resistant even when exposed to liquids and whensubjected to physical contact and manipulation that are encounteredduring the course of an operation. A laparotomy sheet is an elongatedgenerally rectangular sheet used to cover the patient during thoracic orabdominal surgery, and is typically about 6 to 8 feet in length andabout 3 to 6 feet in width. The layer or film of fluid imperviousplastic prevents the liquid encountered during operating procedures fromstriking through the sheet and thereby prevents passage of bacteriathrough the sheet. Moreover, the foam material has a high frictionalcoefficient that prevents dislodgement of surgical instruments, suppliesand the like when placed on the surface of the sheet during anoperation. The foam material is stable at conditions encountered duringsterilization treatments either by steam or ethylene oxide or the like,and the combination of film and foam material has good drapingcharacteristics which are desirable for conforming the drape to the patient during an operation. The open cell foam material is also fluidabsorbent to minimize fluid run-off that is invariably encounteredduring most operations.

When drapes are used in anesthetizing locations, it is of utmostimportance to prevent sparking due to the buildup of static electricalcharges on the drapes, which can be hazardous since explosiveanesthetizing gases and oxygen are often present in operating rooms. Thegoverning criteria for electrical surface resistivity of fabrics used inanesthetizing locations is set forth in the Code for the Use ofFlammable Anesthetics, 1960) published by the National Fire ProtectionAssociation in their publication No. 56 (hereinafter referred to as theCode). Appendix A, Section 35 1 3-Textiles, requires that the surfaceresistivity of the fabric should be measured at an ambient relativehumidity of 50 percent and temperature of 23C by method 76-59 of theAmerican Association of Textile Chemists and Colorists (U.S.A.C.L. 14.112-1961) and states that the measured value should be less than 5 X 10ohms per square unit of the material.

Although many chemical treatments are known to provide antistaticproperties when applied to hydrophobic fibers, films and other surfaces,many of such treatments have been found to be deficient in one or morerespects. For example, some compounds are simply unsuitable in that theyfail to provide sufficient con ductivity or, in other words, fail tolower the surface resistivity to acceptable limits or values thatsatisfy the hereinbefore identified standard when applied to materialsused in locations that have flammable anesthetics. Other chemicals aresoluble only with isopropanol, which is flammable and thus creates ahazardous environment and may require expensive explosion proofprocessing equipment for its use. Additionally, other antistatic agents,when applied to foam materials, exhibit a severe latheringcharacteristic when treated material is rubbed with water present on thematerial. Still other chemical treatments are unsuitable because theiruse during the process of treating ,the material is accompanied by thepresence of irritating vapors. Simi larly, with some chemicals theresulting treated material may cause dermatological problems withpatients or others coming in contact therewith.

One chemical that is available as an antistatic agent is a fatty acidtertiary amine having the structural formula:

wherein R signifies an alkyl group containing from 12 to 18 carbonatoms. While the alkyl group may be a mixture of various fatty acids,one desirable source is tallow. A tallow tertiary amine having the abovestructural formula is supplied by the Armour Industrial ChemicalCompany, Chicago, Illinois under the tradename Ethomeen T/l2. TheEthomeen T/12 tallow fatty acid is sold as an antistatic agent for useon most hydrophobic fibers and is also known to have surfactant orwetting action properties.

Another source of an antistatic agent including a fatty acid tertiaryamine is sold by Paint Products Laboratory of Chicago, Illinois, underthe tradename of Statex PC319. This product, comprising a fatty acidtertiary amine partially neutralized to the correspond-. ing ammoniumsalt, has been used, for example, as an antistatic treatment for nylon,other textiles and airplane windows. While use of this material doesreduce the surface resistivity of acceptable levels when applied to foammaterial, the treated foam does exhibit the undesirable latheringcharacteristic when vigorously rubbed with water present on the foammaterial.

It is a primary object of the present invention to provide a disposablesurgical drape having an open celled foam material on the outer surfacein at least the primary operative area, wherein the foam material istreated to provide significantly improved desirable attributes.

More specifically, it is an object of the present invention to providean improved surgical drape of the hereinbefore described type whereinthe foam material is treated to equal or exceed surface resistivityvalues that are required for use in operating rooms or the like.

Still-another object of the present invention provides for a surgicaldrape wherein the foam material is treated to produce the abovementioned surface resistivity and additionally exhibits superior ratesof fluid absorbency.

Yet another object is to provide a surgical drape that exhibits theabove desirable attributes, but which does not exhibit sudsing orlathering characteristics when rubbed with water present on the foammaterial.

A still further object of the invention lies in the provision of animproved surgical drape having all of the aforementioned desirablecharacteristics and yet which can be produced at such a low cost as topermit disposal of the drape after a single use.

A related object is to provide an improved surgical drape that enablesthe use of relatively low cost hydrophobic foam material, and yetresults in superior rates of fluid absorption comparable to thoseexhibited by more expensive hydrophillic foam material.

Other objects and advantages of the invention will become readilyapparent from'the ensuing detailed description and accompanyingdrawings, in which:

FIG. 1 is a plan view of a surgical drape embodying the presentinvention; and 1 FIG. 2 is a section taken generally along the line 22in FIG. 1.

While the invention is susceptible of various modifications andalternative forms, certain specific embodiments thereof have been shownby way of example in the drawings and will be described in detailherein. It should be understood, however, that it is not intended tolimit the invention to the particular forms disclosed, but on thecontrary, the intention is to cover all modifications, equivalents andalternatives falling within the spirit and scope of the invention asexpressed in the appended claims. In this connection, a laparotomy drapesheet has been shown in the drawings. It should be understood that othertypes of drape sheets may be used and that the invention is not limitedto the type of drape sheet illustrated. Similarly, the specificembodiment of the base sheet is described as comprising outer layers ofcellulosic wadding and inner layers of highly drafted fibers. It shouldbe understood that the construction of the base sheet should notbe'limited to the specific base sheet disclosed.

Turning now to the drawings, there is shown a surgical drape having aprimary operative area, which is the fenestration area of theillustrated laparotomy sheet.

The drape has a fibrous base sheet 10, over which a fluid imperviousplastic layer or film 11 is bonded. The film 11 may be bonded to thefibrous base sheet 10 by any suitable means, such as by means of anadhesive. The film 11 provides a fluid impervious barrier in the primaryoperative area so that any fluids contacting this area cannot strikethrough the sheet. This prevents the transfer of bacteria through thesheet and thereby helps insure that sterile conditions will bemaintained in the primary operative area. It should be understood thatthe film must be capable of remaining stable under the conditionsencountered in the particular treatment to which'the drape sheet issubjected to render it sterile, e.g., temperatures of about 270F forsteam sterilization or about l60F for sterilization by means of ethyleneoxide or the like.

Examples of suitable films are polyethylene e.g., 2 mil. polyethylenefilm manufactured by Clopay Corp, Cincinnati, Ohio; polypropylene, e.g.,Extrel II available from Extrudo Film Corp, New York, New York;polyethylene methylacrylate copolymer film manufactured by EdisonPlastics Company; and vinyl chloride films. The film should besubstantially free of pin holes to provide the desired sterilitybarrier, and thus must generally be at least 0.15 mil thick.

Overlying the fluid impervious film 11 is a foam ma terial 12 which maybe bonded to the film 11 by any suitable means, but preferably bymeansof an adhesive. The absorbency of the open celled foam l2 preventsexcessive fluid run-off and yet the absorbed fluids cannot strikethrough the drape because of the intermediate layer of fluid imperviousfilm 1 l. The relatively high coefficient of friction of the foammaterial provides a substantially non-slip surface which preventsaccidental dislodgement of surgical instruments and the like when theyare placed on the surface of the foam material. In addition, the foammaterial 12 preferably has a low glare which is achieved in part by itsopen cellular structure and which may be enhanced by tinting or coloringthe foam during its manufacture or subsequently. The foam thicknesswould generally be in the rangeof about 25 mils to about mils, and theabsorbency of the foam sheet should be at least about percent by weightand for a 40 mil thick foam material preferably at least 575 percent andat least 4.5 gm/4 inch by 4 inch sample. Examples of suitable foams are40 mil polyester polyurethane foam having a density of 1.7 lbs/ftavailable from Reeves Brothers Inc., New York, New York or TennecoChemicals Inc., New York, New York and polyether polyurethane foams.

The base sheet 10 preferably comprises outer layers of cellulosicwadding and inner layers of highly drafted fibers disposed angularlyrelative to each other. A spaced pattern of adhesive is disposed betweeneach fiber layer and its. adjacent wadding layer with the fibers in eachlayer partially embedded in and held by the adhesive in the adjacentadhesive layer and partially embedded in and held by the adhesive in theouter adhesive layer where it extends between the fibers of its adjacentfiber layer and with a portion of the adhesive in both adhesive layersjoined where the adhesive patterns are superimposed. This -material isdescribed in more 'detail in copending Sokolowski et al 1 applicationSer. No. 546,067, filed Apr. 28, 1966 now US. Pat. No. 3,484,330 andassigned to the assignee of the present invention.

Suitable adhesives foruse in bonding the foam material to the film andfor bonding the film to the base sheet are preferably waterresistantadhesives that are solvent based, in solvents such as, forexampleymethyl ethyl ketone or ethyl acetate. One-adhesive is a twocomponent urethane solvent basedsystcm', available from the ChemicalDivision of Borden, Inc. Chicago, Illinois under the tradename MA-5750.The adhesive is suitably applied to the film at a loading of about 2 tograms per square yard and may be applied at room temperature. Theadhesive is preferably applied in a spaced pattern to maintainflexibility. The pressure used to laminate the film to the foam materialis rela tively light, and is just sufficient'to make good contactbetween the film and foam material. While the bonding of the film to thebase sheet may. be performed using similar adhesive and loading, theadhesive is preferably continuous around the fenestration and around theouter periphery of the film.

In accordance with the present invention, the foam material 12 istreated with an isopropanol-water solution of a fatty acid tertiaryamine, partially neutralized to a carefully controlled level to thecorresponding. am monium salt to achieve the necessary surfaceresistivity superior'rate of fluid absorbency and yet obviate theundesirable lathering property. I

The treating solution thus includes the reaction product of a fatty acidtertiary amine having the structural formula: i 3

(wherein R signifies an alkyl group containing from 12 to 18 carbonatoms) and a mineral acid, Among the mineral acids that can be used arehydrochloric acid, sulfuric acid and phosphoric acid, althoughphosphoric acid is preferred. The alkyl group may consist of a singlemember or the amine may comprise a mixture having different alkylgroups. In the latter instance, it has been found desirable to usetallow as the source for R, viz.- the alkyl group.

In keeping with the present invention, the reaction product ispreferably applied in an isopropanol water solution in sufficientquantity such that at least 0.125 gms/yd addon is applied to the surfaceof the foam material. Although the solution may be sprayed upon thesurface of the foam material, it has been found that flexographicprinting of the solution is preferred, due to the fact that quantitiesare more easily controlled and there is less potential for creating ahealth hazard in terms of explosive vapor concentrations than may bepresent if the solution is sprayed upon the surface of the foammaterial. The particular solvent in which the compound is dissolved hasbeen found to be important. It is preferred to use an isopropanol-watersolvent wherein the isopropanol comprises between about 30 and 80percent by weight of the solvent. If less than about 30 percentisopropanol is used, it has been found difficult to dissolve thecompound. If more than 80 percent isopropanol is used, the antistaticproperties of the resulting drape may be decreased below acceptablelimits as set forth in the hcreinbefore mentioned Code.

Since the fatty acid tertiary amine is known to be a wetting agent orsurfactant, it would be expected that 6 the free amine is the cause ofthe lathering or sudsing characteristic. It would accordingly be assumedthat the lathering characteristic would be minimized by tying up orneutralizing the free amine. Thus, it would be anticipated that thegreater the extent of neutralization (causing a concomitant reduction inthe pH), the less lathering or sudsing would be a problem. Contrary toexpected belief, however, it has been found that neutralization mustonly be carried out to a certain level, because further neutralizationin fact results in the unwanted lathering property in the treated drape.

To achieve the objectives of the present invention, the amounts ofmineral acid and amine should thus be controlled to provideneutralization of the amine to an extent not greater than about 34percent. In keeping with the present invention the degree ofneutralization can be obtained by maintaining the. pH within carefullycontrolled limits. To this end, by insuring that the pH does not dropbelow about 7.5 (as measured by a pH meter haying water in the probes)desired neutralization will result.

Where phosphoric acid is used and the pH of the treatmentis about 7.5 orgreater, it is believed that the principal reaction product'ha-s' thefollowing structural formula I i wherein R, signifies an alkyl groupcontaining from 12 to 18 carbon atoms. u

In accordance with a further aspect of the present invention, it. hasbeen found that if the solution has a pH of greater than about 85, it ismore difficult to dissolve the reaction product in the solvent unlessthe solvent contains a greater amount of isopropanol and, additionally,the reaction product tends to precipitate out. As previously mentioned,the antistatic properties of the foam may be impaired if the percentageof isopropanol in the solvent exceeds about percent.

In keeping with the present invention, it has been found that thetreatment of the foam material with the above mentioned reaction productalso significantly improves the rate of absorption of liquids that comein contact with the foam material. While an open celled foam material,even if it is normally hydrophobic, will absorb fluids, normallyhydrophobic open celled foam material often requires considerable timebefore the fluid is absorbed into the cellular structure of foammaterial. It should be understood that the rate of absorbency of thefoam material is important since any liquids that come in contact withthe foam material during an operation should preferably be readilyabsorbed rather than remain on the foam material surface where aphysician or other member of a surgical team would contact the fluid.Although polyurethane foam having some degree of hydrophilicity iscommercially available, the cost of such foam is substantially greaterthan commercially available hydrophobic polyurethane foam material. Thepresent invention, in addition to providing surface resistivity valueswithin the prescribed range as required by the Code, has the additionaleffect of providing greatly increased rates of fluid absorption, all ofwhich may be achieved at a much lower cost since normally hydrophobicfoam material may be used.

As one specific example of treating the foam material in accordance withthe present invention, a disposable surgical drape having exposed 40 milpolyester polyurethane, open celled foam material was treated with aisopropanol water solution of the reaction product of the tallow fattyacid tertiary amine and phosphoric acid with the solution being adjustedto have a pH of about 7.5. The isopropanol-water solvent contained about40 percent isopropanol and approximately 6.2 percent solids of thetallow fatty acid tertiary amine that was about 34 percent neutralizedto the tallow fatty acid ammonium salt with phosphoric acid. Thesolution was printed upon the outer surface of the foam material suchthat about 0.125 gm/yd add-on of the reaction product was present afterdrying to eliminate the solvent. It was found that the rate of waterabsorbency as measured by placing drops of water on the surface and.measuring the time required for it to be absorbed into the foammaterial was less than a few seconds the majority of the time ascompared to in excess of 300 seconds for untreated hydrophobicpolyurethane foam. Similar tests were run to measure the rate ofabsorption for drops of 1 percent sodium chloride solution which isgenerally known as saline solution often used in surgical operations.Drops of the saline solution were generally absorbed in about 1 to 7seconds as compared to in excess of 300 seconds for untreatedpolyurethane foam material. Surface resistivity values of the treatedfoam material measured in accordance with AATCC test method 76-1969 wereabout 1 X 10 ohms per square unit as compared to about X ohms fornontreated foam. The foam material did not exhibit foaming when it wasvigorously rubbed in the presence of water.

Thus the disposable surgical drape of the present invention has beenshown to exhibit superior rates of absorption characteristics as well assatisfy the surface resistivity requirements of the National FireProtection Association and failed to exhibit the unwanted latheringcharacteristics.

What is claimed is:

1. In a disposable surgical drape having a primary operative area, saiddrape comprising a fibrous base sheet, a fluid impervious plastic layercovering said primary operative area, the improvement comprising a sheetof flexible, normally hydrophobic, open celled foam material bonded tothe outer surface of said plastic layer, said foam material having beentreated with the reaction product of a mineral acid and a fatty acidtertiary amine, said fatty acid tertiary amine being neutralized lessthan about 34 percent to form a fatty acid tertiary ammonium salt, saidfatty acid tertiary amine having the structural formula:

where R signifies an alkyl group containing from 12 to 18 carbon atoms;said compound being effective to render said foam material antistatic,while providing increased rates of fluid absorption and reduced tendencyfor lathering when said foam material is vigorously rubbed in thepresence of water.

2. In a disposable surgical drape as defined in claim 1 wherein saidreaction product is present in excess of about 0.125 gms/yd and thesurface resistivity of the treated foam material is less than about 5 X10 ohms.

3. In a surgical drape as defined in claim 1, wherein said mineral acidis selected from the group consisting of phosphoric acid, hydrochloricacid and sulfuric acid.

4. In a surgical drape as defined in claim 1 wherein said foam materialis a polyurethane foam.

1. IN A DISPOSABLE SURGICAL DRAPE HAVING A PRIMARY OPERATIVE AREA, SAIDDRAPE COMPRISING A FIBROUS BASE SHEET, A FLUID IMPERVIOUS PLASTIC LAYERCONVERING SAID PRIMARY OPERATIVE AREA, THE IMPROVEMENT COMPRISING ASHEET OF FLEXIBLE, NORMALLY HYDROPHOBIC, OPEN CELLED FOAM MATERIALBONDED TO THE OUTER SURFACE OF SAID PLASTIC LAYER, SAID FOAM MATERIALHAVING BEEN TREATED WITH THE REACTION PRODUCT OF A MINERAL ACID AND AFATTY ACID TERTIARY AMINE, SAID FATTY ACID TERITARY AMINE BEINGNEUTRALIZED LESS THAN ABOUT 34 PERCENT TO FORM A FATTY ACID TERTIARYAMMONIUM SALT, SAID FATTY ACID TERTIARY AMINE HAVING THE STRUCTURALFORMULA:
 2. In a disposable surgical drape as defined in claim 1 whereinsaid reaction product is present in excess of about 0.125 gms/yd2 andthe surface resistivity of the treated foam material is less than about5 X 1011 ohms.
 3. In a surgical drape as defined in claim 1, whereinsaid mineral acid is selected from the group consisting of phosphoricacid, hydrochloric acid and sulfuric acid.
 4. In a surgical drape asdefined in claim 1 wherein said foam material is a polyurethane foam.